The main objective of this research is to understand at the molecular level the DNA: protein and protein: interactions that underlie the basic genetic process of DNA replication. The DNA replication proteins essential for DNA chain elongation and fork movement of the bacteriophage T4 have already been identified and purified to near homogeneity. When these proteins are incubated in vitro, a replication apparatus can be reconstructed that mimics most of the charcteristics of an in vivo DNA replication fork. Analysis of the partial reactions that comprise DNA chain elongation and fork movement with this protein apparatus are now underway to elucidate the details of this mechanism. It is proposed to expand the study of this very successful model system to include the T4 chromosome initiation process whereby replication forks are generated at specific DNA sites in vivo. The proteins that recognize a T4 origin and transform this DNA site into the DNA replicative "eye" form will be identified and purified. Maximum use will be made of T4 genetics and previous studies that provide an excellent catalogue of available T4 DNA replication mutants from which to choose. Those factors will be sought which provide the minimal necessary structure to get biologically correct DNA initiation at the T4 origin(s). These factors combined with T4 chain elongation-fork movement proteins aleady isolated should enable the entire DNA replication mechanism to be carried out in vitro from DNA origin site recognition on the parental duplex DNA through progeny replication.